The operation of internal combustion engines using gaseous fuels requires properly adapted devices and mixing methods for forming a fuel-air mixture, as well as for supplying this mixture to the combustion chamber in the cylinders of the internal combustion engine. The gaseous fuel is mixed for the most part upstream from the combustion chamber in the area of the air intake passages and then flows during the intake stroke into the combustion chamber(s) of the internal combustion engine. The European Patent 309 044 B1 already discloses a mixture and regulating device of this type, which is arranged in the engine air-intake line. Air and gaseous fuel are thereby mixed in a so-called venturi tube, and this fuel-air mixture then flows, as is generally known, into the engine. As is apparent from this known device, it is relatively expensive and difficult to regulate the mixture ratio, and there is no guarantee of a thorough and uniform intermixing of air and gaseous fuel. The result is uneven combustion of the mixture in the combustion chamber of the engine, so that no optimal energy utilization is possible and undesirable pollutants are formed. To ensure an effective combustion of the gas-air mixture in the combustion chamber, additional measures are, therefore, needed to generate a turbulent flow of the mixture, the aim being to achieve a thorough intermixing and rapid combustion. As is known, additional turbulence is generated when the mixture stream flows at the end of the intake passage through the annular gap between the valve and the valve seat at the cylinder head, through which means a conical mixture spray is formed. It is also known to increase turbulence by applying a rotational energy to the mixture stream flowing into the cylinder by shaping the intake passage accordingly or by installing interior components upstream from the intake valve. Furthermore, a so-called squish effect is produced in the cylinders of present-day engines in that as the piston approaches the top dead center between the piston and the cylinder head, a narrower and narrower gap is formed, so that the mixture is squeezed out of this gap into a central combustion chamber recess. This also has the effect of intensifying turbulence. The disadvantage associated with all of these known measures for increasing turbulence in the combustion chamber is that the intensity of the turbulence varies more or less in proportion to the engine speed. This is because the velocity of the air, gas, and mixture flows changes in response to variations in engine speeds. Therefore, at low speeds, the turbulence is weak and, accordingly, combustion is poor. This effect becomes especially pronounced when natural gas is used as fuel and/or when a lean mixture is used. However, at high speeds, the flow velocities are so high that it is more difficult to ignite the mixture. At high speeds, that is at high flow velocities, an intensive vortex flow through the intake valve also results in a considerable loss of pressure, so that cylinder charging and, thus, power output are diminished. To compensate for these disadvantages, compromises have to be made, for the most part, when working the internal combustion engines that use gaseous fuels, or additional complicated and expensive measures have to be resorted to.